1. Field of the Invention
The present invention relates to a disc brake with a parking brake mechanism, and more particularly to a disc brake with a parking brake mechanism in which a cup-shaped piston is axially slidably disposed in a cylinder defined in a caliper with a piston seal interposed, the piston being movable by the parking brake mechanism or a fluid supplied under pressure to the cylinder for pushing the brake pads.
2. Description of the Prior Art
One known disc brake of the type described above is disclosed in U.S. Pat. No. 3,783,981 and shown in FIG. 1 of the accompanying drawings. The prior disc brake includes a parking brake mechanism composed of an adjusting bolt 2 disposed coaxially in a cup-shaped piston 1 and secured thereto, an adjusting nut 5 threaded over the adjusting bolt 2 and connected by a thrust bearing 3 to a bottom 4b of a cylinder 4a defined in a caliper 4, a spring 7 having a lefthand end (as shown) engaging a tubular retainer 6 fixed to an inner peripheral wall of the cylinder 4a for normally urging the adjusting nut 5 to the right, a thrust bearing 8 interposed between the spring 7 and the adjusting nut 5, a piston 9 axially slidably fitted in a bore 4c defined coaxially in the cylinder 4a and confronting the adjusting nut 5 with a clearance S therebetween, a cam shaft 10 rotatably supported in the caliper 4 behind the piston 9 and having a cam slot 10a opening toward a recess 9a in a rear end of the piston 9, and a toggle 11 interposed between the cam shaft 10 and the piston 9 and interconnecting them.
When the piston 1 is pushed to the left by a fluid supplied under pressure into the cylinder 4a, the adjusting nut 5 is caused to rotate with respect to the adjusting bolt 2 moving with the piston 1 by the coaction of the spring 7 and the thrust bearing 8 for automatically adjusting a so-called pad clearance. By pushing the piston 1 into the cylinder 4a upon replacement of a pad, the adjusting nut 5 is rotated by the action of the thrust bearing 3 to bring the piston 1 and the adjusting bolt 2 back to the illustrated initial position without being rotated. Therefore, pad replacement can be effected efficiently, and there is no danger of a piston seal 12 being torn off by the piston 1.
With the known disc brake, however, many parts of the parking brake mechanism such as the adjusting bolt 2, the thrust bearing 3, the adjusting nut 5, the retainer 6, the spring 7, and the thrust bearing 8 are accommodated in the cylinder 4a, forming a complex air trapping space within the cylinder 4a from which air cannot easily be discharged.